Process for preparing polymeric films useful for blocking the transmission of near infra red light

ABSTRACT

The present invention is an infra red (IR)-blocking coating and a process for applying the IR-blocking coating onto the surface of a polymer. The process comprises the steps of dispersing an IR-blocking material in a mixture of solvent comprising a dissolved polymer and using standard printing processes to coat at least a portion of the surface of a bulk polymer, preferably a sheet or film. The present invention also provides safety glass laminates whose polymer interlayers have improved adhesion to glass in addition to light blocking properties.

This application claims the benefit of U.S. Provisional Application No.60/529,853, filed Dec. 15, 2003, which is incorporated by referenceherein for all purposes as if fully set forth.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to films useful for blocking infrared (IR) and/ornear infra red (NIR) light. This invention particularly relates topolymers having IR and/or NIR-blocking coatings on at least a portion oftheir surface and to a process for preparing same.

2. Description of the Related Art

Several patents and publications are cited in this description in orderto more fully describe the state of the art to which this inventionpertains. The entire disclosure of each of these patents andpublications is incorporated by reference herein.

There is growing interest in means of controlling solar heat gain inautomobiles and buildings. Various coated glasses have been proposed toreduce solar heat gain through windows. These coatings, however, whichare generally thin films of silver or other metallic compounds, alsogenerally block out electromotive energy. This effect rendersinoperative various modern necessities such as cell phones, globalpositioning satellite (GPS) units, and automatic toll takers on tollroads. It has been demonstrated, however, that electromotive energy canpass through treated windows when the blocking particles are wellseparated from one another.

Coatings comprising dispersed blocking particles and disposed on glassor other substrates are well known. See, for example, U.S. Pat. No.5,518,810; U.S. Pat. No. 6,579,608; and U.S. Pat. No. 6,506,487. Theseparticles can include UV absorbing compounds, visible colored pigments,NIR (heat) absorbing compounds, or any combination of these entities.However, the energy blocking coatings known in the art generally havepoor adhesion to some polymeric surfaces, particularly polyvinyl butyral(PVB). Good adhesion between the polymer interlayer and both the energyblocking coating and the glass are necessary requirements forappropriate functionality in a laminated safety glass. Adhesion that istoo low can lead to exfoliation of the safety glass laminates, whileadhesion that is too high can lead to impact failures.

SUMMARY OF THE INVENTION

In one aspect, the present invention is a polymer having a surface thatis at least partially covered with a coating comprising infra redblocking particles, wherein the polymer is in the form of a film orsheet.

In another aspect, the present invention is a composition which is adispersion comprising Indium Tin Oxide (ITO) and polyvinylbutyral indimethyl formamide (DMF).

In another aspect, the present invention is a process for preparing apolymeric film or sheet having at least one surface that is at leastpartially covered with a coating comprising infra red blockingparticles. The IR blocking coating is applied by a process comprisingthe steps of: (1) dispersing the IR blocking particles in a mixture ofPVB and dimethyl formamide (DMF) to obtain an IR blocking ink; (2)printing the IR blocking ink onto at least a portion of the polymericsurface.

In still another aspect, the present invention is a process forpreparing a polymeric film or sheet having at least one surface that isat least partially covered with a coating comprising infra red blockingparticles, wherein the IR blocking coating comprises IR blockingparticles dispersed in PVB, comprising the steps: passing a mixture ofIR blocking particles, dimethyl formamide (DMF), and PVB through agrinding apparatus to disperse the IR blocking particles and obtain anIR blocking ink; and printing the ink onto the surface of the polymerfilm or sheet.

In another aspect, the present invention is a laminate comprising apolymeric film or sheet wherein the film or sheet comprises at least onesurface that is at least partially covered with an IR blocking coatingcomprising IR blocking particles and PVB.

In still another aspect, the present invention is a laminate comprisingat least two layers of a polymeric film or sheet, at least one of saidtwo layers having at least one surface that is at least partiallycovered with an IR blocking coating comprising IR blocking particles andPVB.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a graph of the light transmission spectra of a series of glasslaminates having PVB sheets that are uncoated or coated with energyblocking coatings.

DETAILED DESCRIPTION OF THE INVENTION

The definitions herein apply to the terms as used throughout thisspecification, unless otherwise limited in specific instances.

The term “solution”, as used herein with respect to liquids containingone or more polymers, refers to liquids in which at least one solute isa polymer, although the soluble polymer and other substances, includingother polymer(s), may also be present in the liquid in undissolved form.

The terms “dispersion” and “suspension”, as used herein, areinterchangeable and refer to a liquid comprising particulate matter. Adispersion may be stable, unstable, or partially stable with respect toprecipitation, flocculation, syneresis, etc.

The terms “energy blocking” and “IR blocking”, as used herein, refers toa property of decreasing the transmission of energy, or, specifically,infra red energy. The blocking may occur by any mechanism, e.g.,absorption, reflectance, etc.

The term “infra red”, as used herein, includes the near infra red.

The terms “finite amount” and “finite value” refer to an amount that isnot equal to zero.

The term “about” means that amounts, sizes, formulations, parameters,and other quantities and characteristics are not and need not be exact,but may be approximate and/or larger or smaller, as desired, reflectingtolerances, conversion factors, rounding off, measurement error and thelike, and other factors known to those of skill in the art. In general,an amount, size, formulation, parameter or other quantity orcharacteristic is “about” or “approximate” whether or not expresslystated to be such.

In one embodiment, the present invention is a polymer which has disposedon at least a portion of its surface a coating of an infra red blockingmaterial that has been previously dispersed in a polymeric matrix. Apolymer suitable for use in the present invention is one that is alsosuitable for use in a laminate with glass, and is preferably useful inarchitectural or automotive glazings. For example, a suitable polymer isone that is transparent to light in the visible region of the lightspectrum. More particularly, suitable polymers include, withoutlimitation, polyesters; polyurethanes; polyvinyl chlorides; polyacetals;polyvinyl butyral (PVB); and acid copolymers and copolymer ionomersobtained from copolymerization of ethylene with an ethylenicallyunsaturated carboxylic acid and/or derivatives thereof. Preferably thepolymer is polyvinyl butyral.

The polymer can be formed into a film or a sheet by conventional methodssuch as by various conventional extrusion methods, including, withoutlimitation, a cast film extrusion process or a blown film extrusionprocess.

The polymer on at least one of its surfaces is at least partiallycovered with a coating comprising an infra red blocking material. Theinfra red blocking material can be any material that interferes with thetransmission of infra red light, preferably particularly near infra redlight. Such materials are known and can be considered conventional. Suchmaterials include, for example, indium tin oxide (ITO), antimony tinoxide (ATO), lanthanum hexaboride, and iron oxides. Preferably the IRblocking material is particulate in form. Typically the particles haveultra fine particles sizes so that the transparency of the laminate isnot adversely affected. Preferably the IR blocking particles of thepresent invention comprise ATO or ITO. Even more preferably, the IRblocking particles comprise ITO.

Those of skill in the art are able to ascertain an appropriate level ofIR blocking particles in the IR blocking coating, based on, e.g., thedesired level of transmittance balanced against physical properties suchas the haze of the coating, or the adhesion of the coated surface toanother surface in a laminate. Preferably, however, the IR blockingmaterial is present in the coating in a finite amount up to about 30 wt%, more preferably from about 10 wt % to about 20 wt %, and still morepreferably about 15 wt % based on the total weight of the dispersion,i.e., of the IR blocking material, the DMF and the polymer.

In the present invention, the IR blocking particles are applied to thesurface of the polymer as a dispersion of the small particles in amatrix comprising an organic solvent, such as dimethyl formamide (DMF)for example, and a polymeric binder. Preferably, the polymeric binder isdissolved in the organic solvent. Preferably the polymeric binder is thesame as or compatible with the polymer being coated. By “compatiblewith”, it is meant that the polymeric binder adheres strongly to thesurface of the polymer being coated. The polymeric binder functions toaid in adhesion of the particles to the polymer surface, and to improveadhesion of the coated polymer to an adjoining layer in a laminate.

Preferably the polymeric binder comprises PVB. More preferably, thepolymeric binder consists essentially of PVB. Still more preferably, thepolymeric binder consists essentially of PVB having about 23% freehydroxyl.

Those of skill in the art will be able to ascertain an appropriate levelof polymeric binder based on the desired properties of the coating.Preferably, however, the polymeric binder is present in a finite amountup to about 20 wt %, more preferably at a level of about 3 to about 13wt %, and still more preferably at a level of about 8 wt %, based on thetotal weight of the IR blocking particle dispersion. Of note are IRblocking coatings comprising about 8 wt % of a 23% free hydroxyl PVB.

In another embodiment, the present invention is a process for applying adispersion of an IR blocking material to at least a portion of thesurface of a polymeric material comprising the step of printing thedispersion onto the surface. Preferably the polymeric material is in theform of a film or sheet. Preferably the printing step is a conventionalprocess such as flexographic or gravure printing. The process cancomprise the step of passing the IR blocking particles through agrinding or milling apparatus, such as an Eiger mill, to reduce theparticle size of the IR blocking material and/or to disperse thematerial in the organic solvent or in the polymer matrix. Accordingly,the IR blocking material can be passed through the grinding apparatusdry, or as a dispersion in the organic solvent, or as a dispersion inthe polymer matrix. The dispersed ink thus obtained can be printed ontoat least a portion of at least one surface of the polymer. Preferablythe ink is printed directly onto a surface of the polymer. The coatedpolymer may optionally be dried by any suitable means known in the art,such as by the application of heat or vacuum of both, for example.

In another embodiment, the present invention is a laminate comprising atleast one polymer layer that is at least partially covered with acoating comprising an IR blocking material. Suitable and preferredpolymer layers and IR blocking coatings are as set forth above. Thelaminate preferably comprises at least one sheet of glass, but cancomprise another material in a rigid transparent layer as a substitutefor glass.

In another embodiment, the present invention comprises a laminate of atleast two polymer layers, at least one of which has been at leastpartially covered with a coating comprising an IR blocking material.Again, suitable and preferred polymer layers and IR blocking coatingsare as set forth above. The sheets can be laminated together asadjoining and adjacent layers, or can be separated by other laminatelayers. The coated polymers can comprise the same materials or differentmaterials, including the same or different IR blocking materials. In apreferred embodiment, the coating or coatings are disposed between twoof the polymer layers. More preferably, the two polymer layers areadjacent. In another preferred embodiment, the laminate includes atleast one outer layer of glass or another material in a rigidtransparent layer as a substitute for glass. More preferably, thelaminate includes two outer layers of glass or another rigid transparentmaterial.

The coated surface of the polymer in a laminate of the present inventioncan be oriented away from the outer surface of the laminate, or towardsthe outer surface of the laminate, or can be the outer surface of thelaminate. Various laminate constructions can be envisioned by one ofordinary skill in the glazing art.

EXAMPLES

The Examples and Comparative Examples are presented for illustrativepurposes only, and are not intended to limit the scope of the presentinvention in any manner.

Example 1

Indium tin oxide (40 gms) is dispersed in 300 gms of a 6.4% PVB in DMFsolution. The dispersion is milled in an Eiger mill at ambienttemperature for approximately 4 hours, or until the mixture appearsuniform in appearance. The dispersion is then coated by hand-dippingonto a sheet of 3GO-based PVB (30 mils) using a rotogravure printingprocess. The web speed was 50 fpm. The PVB sheet was imprinted with upto four layers of the the ITO dispersion. Samples were cut from theprinted PVB sheet after each of the printing passes.

The samples of the coated PVB sheet were laminated between two layers ofclear glass, thickness 2.3 mm. The glass laminates are tested bymeasuring haze, pummeling, and the transmittance of light havingwavelengths in the range of from 275 to 2500 nm.

The light transmittance results of a similar experiment, which are shownin FIG. 1, clearly demonstrate that the transmittance of light at longerwavelengths, including NIR wavelengths, decreases significantly uponapplication of a coating of the invention. Moreover, the transmittancedecreases even further with increasing levels of ITO.

While certain of the preferred embodiments of the present invention havebeen described and specifically exemplified above, it is not intendedthat the invention be limited to such embodiments. Various modificationsmay be made without departing from the scope and spirit of the presentinvention, as set forth in the following claims.

1. A polymer having a surface that is at least partially covered with acoating comprising infra red blocking particles, wherein the polymer isin the form of a film or sheet.
 2. The polymer of claim 1, wherein theinfra red blocking particles comprise a material selected from the groupconsisting of indium tin oxide (ITO), antimony tin oxide (ATO),lanthanum hexaboride, and iron oxides.
 3. A composition which is adispersion comprising Indium Tin Oxide (ITO) and polyvinylbutyral indimethyl formamide (DMF).
 4. The composition of claim 3, comprising 8 wt% of 23% free hydroxyl polyvinylbutyral.
 5. A process for preparing apolymeric film or sheet having at least one surface that is at leastpartially covered with an infra red blocking coating comprising the stepof applying the infra red blocking coating to the polymeric film orsheet by printing.
 6. The process of claim 5 wherein the infra redblocking coating is applied as an ink comprising an infra red blockingmaterial, polyvinylbutyral, and dimethyl formamide.
 7. The process ofclaim 5 wherein the infra red blocking coating comprises an infra redblocking material selected from the group consisting of indium tin oxide(ITO), antimony tin oxide (ATO), lanthanum hexaboride, and iron oxides.8. A process for preparing a polymeric film or sheet having at least onesurface that is at least partially covered with a coating comprisinginfra red blocking particles, wherein the IR blocking coating comprisesIR blocking particles dispersed in PVB, the process comprising thesteps: passing the IR blocking particles through a grinding apparatus todisperse the IR blocking particles and obtain an IR blocking ink; andprinting the ink onto the surface of the polymer film or sheet.
 9. Theprocess of claim 8, wherein the IR blocking particles are passed throughthe grinding apparatus with dimethyl formamide, polyvinylbutyral, orboth dimethyl formamide and polyvinylbutyral.
 10. The process of claim8, wherein the IR blocking particles comprise an infra red blockingmaterial selected from the group consisting of indium tin oxide (ITO),antimony tin oxide (ATO), lanthanum hexaboride, and iron oxides.
 11. Alaminate comprising a polymeric film or sheet wherein the film or sheetcomprises at least one surface that is at least partially covered withan IR blocking coating comprising IR blocking particles and PVB.
 12. Thelaminate of claim 11 wherein the IR blocking particles comprise an infrared blocking material selected from the group consisting of indium tinoxide (ITO), antimony tin oxide (ATO), lanthanum hexaboride, and ironoxides.
 13. A laminate comprising at least two layers of a polymericfilm or sheet, at least one of said two layers having at least onesurface that is at least partially covered with an IR blocking coatingcomprising IR blocking particles and PVB.
 14. The laminate of claim 13,wherein the IR blocking particles comprise an infra red blockingmaterial selected from the group consisting of indium tin oxide (ITO),antimony tin oxide (ATO), lanthanum hexaboride, and iron oxides.